The present disclosure relates generally to internal combustion engines. In particular, improvements to the design of the interface between pistons and the crankshaft of internal combustion engines in a radial configuration are described.
It is well known in the general aviation industry that the trend is towards a reduction of pilots and flights due to high expenses in nearly all aspects of aviation, and lower operational costs are needed at a minimum to reverse this trend. One aspect of increasing concern to the future viability of widespread general aviation is the cost and availability of fuel. The vast majority of lower cost general aviation planes use reciprocating engines that burn avgas, a highly-refined version of the gasoline used in cars. Because of its specialized and limited purpose, the price of avgas is continually increasing, while its long term availability is also in question. Because of these factors, confidence in the current state of reciprocating aviation engines is in decline. Thus, an advanced piston engine design that can burn cheaper and more readily available Jet-A can bring benefits of reduced operational cost, reduced environmental impact and foster improvements in airframe design, all of which will aid in the reversal of the decline of general aviation.
Once such promising design is a compression-ignition (diesel) radial engine. A radial engine configuration has a set of cylinders arranged radially in a single plane around a common crankshaft hub. Examples of alternative engine configurations include inline, V and opposed. In comparison to these alternative configurations, a radial configuration has superior engine density, which results in a superior power to weight ratio, desirable for aircraft propulsion purposes. This can be greatly enhanced by implementing the engine using a two-stroke combustion cycle, with fuel being burned with each down stroke of each piston, as opposed to every other down stroke as required by a four-stroke combustion cycle.
Known radial engine configurations are not entirely satisfactory for the range of applications in which they are employed, however. For example, existing radial engines typically employ some version of a master-and-articulating-rod assembly, with one cylinder possessing a master connecting rod that typically bolts to a crankshaft throw, the connecting rods for the remaining cylinders attaching around the master connecting rod, to which in turn are attached each of the pistons. This configuration adds complexity, weight to the drive train, presents a myriad of failure points, and prevents a uniform piston motion. By using a two-stroke combustion cycle, a simpler, lighter alternative can be implemented: a connecting rod with a slipper bearing design, where the slipper is a portion of a circle (arc segment) that interfaces directly with the crankshaft throw. However, because each piston typically lies in a common plane, the size of the slipper is limited by the need to avoid collision with the slippers of adjacent connecting rods. Moreover, as the number of cylinders in the common plane increases, the maximum slipper size and corresponding contact area with the crankshaft decreases. As each slipper is responsible for transmission of power from its piston during combustion, smaller slippers will wear faster and be more prone to failure due to the concentration of force in an increasingly smaller area. Thus, it is generally accepted in the prior art that there can be no more than four cylinders in a given cylinder plane and still maintain an acceptable amount of slipper to crankshaft contact area, which in turn severely limits the scalability of a radial engine employing a slipper bearing design.
Thus, there exists a need for improved radial engine piston-crankshaft interfaces that improve upon and advance the design of known slipper bearing designs. Examples of new and useful radial engine piston-crankshaft interfaces relevant to the needs existing in the field are discussed below.
Disclosure addressing one or more of the identified existing needs is provided in the detailed description below. Examples of references relevant to improved radial engine piston-crankshaft interfaces include U.S. Pat. Nos. 5,197,416 and 2,199,655. The complete disclosures of the above patents and patent applications are herein incorporated by reference for all purposes.